1. Field of the Invention
The invention relates to a technique for an electrostatic coating gun that is able to selectively use a plurality of types of coatings.
2. Description of Related Art
In an existing art, in order for an electrostatic coating gun to be able to perform coating while changing a plurality of types of coatings in a short period of time, there is known a multicolor coating gun that includes a color change valve (hereinafter, abbreviated as CCV) for changing among a plurality of coatings. In addition, in recent years, when a multicolor coating gun is used, in order to reduce a time required for color change, a multicolor coating gun in which a color change valve unit (hereinafter, referred to as CCV unit) having a plurality of CCVs is arranged inside a casing that contains an air motor, or the like, of the coating gun has been employed, and the technique for such a multicolor coating gun is described in Japanese Patent Application Publication No. 2007-50336 (JP-A-2007-50336) and is publicly known.
In the coating gun according to the related art described in JP-A-2007-50336, the CCV unit is arranged immediately behind the air motor inside the casing that contains the air motor to minimize a path for supplying a coating from the CCV unit to a bell cup. With the above configuration, it is possible to minimize the amount of coating remaining in the path for supplying a coating from the CCV unit to the bell cup, so it is possible to reduce a time required for color change and reduce wasted coatings.
Usually, high voltage is applied by a high-voltage generating device to the air motor, the bell cup, and the like. The air motor is contained in the casing of the electrostatic coating gun. The bell cup is supported by the air motor. In addition, a robot arm that displaceably supports the coating gun is generally connected to a ground, and the potential of the robot arm is kept at “0”. Therefore, in the existing electrostatic coating gun, there is a difference in potential between a portion, such as the air motor, to which high voltage is applied (hereinafter, referred to as high-voltage region) and a grounded portion of the coating gun (hereinafter, referred to as a grounded region), so the air motor (high-voltage region) needs to ensure a sufficient distance that does not cause a dielectric breakdown (that is, insulation distance) from the grounded region. Note that the “insulation distance” here is a concept including a creepage distance and a spatial distance.
In the coating gun described in JP-A-2007-50336, the same high voltage as that applied to the air motor is also applied to the CCV unit, and the CCV unit also belongs to the high-voltage region, so it is necessary to ensure the insulation distance between the CCV unit and the grounded region. Then, in such a case, in order to ensure the insulation distance between the CCV unit and the grounded region, it is necessary to take measures, such as increasing the size of the casing. When the CCV unit is contained in the casing of the coating gun, it is difficult to construct a compact electrostatic coating gun.